Coordinated Control of PV-Ultracapacitor System for Enhanced Operation Under Variable Solar Irradiance and Short-Term Voltage Dips

Utilization of an ultracapacitor (UC)-based energy storage device can provide one of the most efficient solutions for short-term operational challenges in grid-connected photovoltaic (PV) systems. This paper proposes an algorithm for coordinated control of PV and ultracapacitor-based energy storage system to minimize the effects of sudden changes in solar irradiance and the presence of low voltages at the point of common coupling. In addition, this work proposes an improved multi-mode operational scheme for control of an ultracapacitor-based energy storage system that takes into consideration various associated limits during charging and discharging modes. The effectiveness of the proposed algorithm in mitigating the impacts of low voltages and short term changes in irradiance is demonstrated using simulation analysis carried out on the modified Consortium for Electric Reliability Technology Solutions (CERTS) microgrid testbed. © 2013 IEEE

An Analytical Approach for Loss Minimization and Voltage Profile Improvement in Distribution Systems with Renewable Energy Sources

Loss minimization and voltage profile improvement are of prime importance in distribution system operation. This paper presents an analytical approach for coordinating distributed energy resources to reduce the active power loss in distribution networks. The proposed approach is based on the network admittance matrix and has an explicit solution if all loads in the network are constant current loads. Furthermore, it is shown that when loads are modeled with other characteristics such as constant power loads, a numerically efficient solution of loss minimization can also be obtained. The resulting solution reduces network losses while ensuring a nominal voltage at the point of common coupling. Case studies on a 19-node distribution system are presented to validate the proposed approach

Impact of non-idealities on the Performance of an Ultracapacitor based Bidirectional DC/DC Converter

This paper analyses the impact of non-idealities on the performance of an ultracapacitor based bidirectional DC/DC converter. In particular, this work analyses the impact of ON state resistance of the MOSFET switches on the performance of bidirectional DC/DC converter. It is shown that, under particular operating conditions, the ON state resistance of the MOSFET can have a significant impact on the performance of th DC/DC converter and can cause an unstable response. An analytical expression is derived to identify the operating conditions under which the non-idealities can have a significant impact on the performance of the DC/DC converter. Simulation results are presented to aid the analysis reported in this paper. © 2020 IEEE

Multimode Operation of a PV-Battery System fed Brushless DC Motor Drive

Utilization of energy storage systems along with Photovoltaic systems, can provide an efficient solution to overcome the challenges associated with renewable energy sources. This paper proposes an algorithm for the multimode operation of a Brushless DC motor drive fed using a combination of Photovoltaic System and battery-based energy storage. Based on the solar irradiation and the state of charge of the battery, the proposed algorithm identifies a control scheme wherein the entire system operates in Four different modes. The working of the PV-Battery System fed Brushless DC Motor Drive under various operating modes is presented and is verified using simulation analysis performed in MATLAB/Simulink. © 2020 IEEE

Computation of Initial Conditions for Dynamic Analysis of a Doubly Fed Induction Machine based on Accurate Equivalent Circuit

A mathematical framework to compute initial conditions of state variables is essential for accurate initialization of dynamic studies. This paper presents an approach for computing initial values of state variables in the dynamic model of a doubly fed induction machine (DFIM). Unlike existing approaches, the proposed approach is based on an accurate equivalent circuit of a DFIM. Time domain simulation results of a standalone DFIM configuration are presented to validate the proposed approach. In addition, the inaccuracy of initial conditions obtained using the existing equivalent circuit is demonstrated using small signal stability analysis of a DFIG

Accurate modeling of doubly fed induction generator based wind farms in load flow analysis

This paper presents an iterative approach for incorporating doubly fed induction generator (DFIG) based variable speed wind farms in steady state studies such as load flow analysis. The proposed approach is based on an accurate steady state equivalent circuit of a DFIG. In the proposed approach, the power flow model of a node with DFIG is determined based on the reference to reactive power control loop of rotor side converter. In addition, the proposed approach takes into consideration various limits associated with the DFIG. Case studies on sample 6-bus system and 418-bus equivalent system of Indian southern grid are presented to validate the proposed approach

Analysis of Filter Design Approaches for Extraction of Instantaneous Symmetrical Components

Extraction of instantaneous symmetrical components plays a vital role in the operation of grid-connected converters. Conventionally, extraction of instantaneous symmetrical components is achieved by transforming the signal into a rotating reference frame and passing it through a digital filter. This work focuses on the design and performance of various digital filters adopted for the extraction of instantaneous symmetrical components. The design considerations and associated trade-offs involved in the design of digital filters are first outlined. Subsequently, the design procedure involved in commonly adopted filtering strategies is reviewed and their performance under various operating conditions is studied. In addition, this work also analyzes the impact of filter design on closed-loop applications such as phase locked loops. © 2022 IEEE

Enhanced modelling of doubly fed induction generator in load flow analysis of distribution systems

This paper presents an accurate framework for incorporating the doubly fed induction generator based wind farms in load flow analysis of distribution systems. The proposed model for doubly fed induction generator is based on an accurate equivalent circuit and also takes into consideration the voltage dependent reactive power limits associated with the doubly fed induction generator. In addition, the developed approach is capable of handling a doubly fed induction generator operating in either maximum power point tracking or non-maximum power point tracking modes. The proposed PQ model of doubly fed induction generator easily fits into the forward–backward technique that is typically employed for obtaining the load flow solution of distribution networks. Test results on 19-bus and 133-bus systems are reported to indicate the effectiveness of the proposed approach

Analysis of Low Voltage Ride Through Techniques for Grid-Connected Photovoltaic Systems

This paper presents a comparative analysis of different low voltage ride though strategies proposed for operation of a grid connected two stage photovoltaic system under low voltages. The existing grid codes mandate that, under the presence of low voltages, a distributed energy resource (DER) must stay connected to the grid for a minimum amount of time. This results in abnormally high currents though the inverter of a PV system, which can potentially damage the semiconductor switches. To avoid this, low voltage ride through techniques are proposed in the literature to ensure that the DER stays connected to the grid. Traditionally, the performance of LVRT techniques is evaluated by assuming an ideal voltage dip at the point of common coupling. In this work, comparative evaluation of different LVRT techniques is carried out on the CERTS test bed with an objective to highlight the impact of network transients on their performance. © 2020 IEEE

Accurate modeling of doubly fed induction generator based wind farms in load flow analysis

This paper presents an iterative approach for incorporating doubly fed induction generator (DFIG) based variable speed wind farms in steady state studies such as load flow analysis. The proposed approach is based on an accurate steady state equivalent circuit of a DFIG. In the proposed approach, the power flow model of a node with DFIG is determined based on the reference to reactive power control loop of rotor side converter. In addition, the proposed approach takes into consideration various limits associated with the DFIG. Case studies on sample 6-bus system and 418-bus equivalent system of Indian southern grid are presented to validate the proposed approach. (c) 2017 Elsevier B.V. All rights reserved